https://bugs.dpdk.org/show_bug.cgi?id=870
Bug ID: 870
Summary: Fragmented packets incorrect RSS distribution with TAP
PMD on Hyper-V platform
Product: DPDK
Version: 20.11
Hardware: x86
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: Normal
Component: ethdev
Assignee: dev@dpdk.org
Reporter: madhuker.myt...@oracle.com
Target Milestone: ---
On Hyper-V based platforms(Azure with Accelerated-mode disabled), the network
ports come up on Failsafe-PMD(and underneath TAP PMD) configured with 4-queues
RSS enabled.
The normal Rx/Tx packets were received and transmitted well. But, when the IP
fragmented packets received on these ports, all the fragments of single-packet
were distributed across different queues, instead of arriving to single-queue.
As per the TAP PMD RSS(based on BPF) algorithm mentioned in the
"tap_bpf_program.c" file, the RSS algorithm written based on 4-tuple(L3 Src/Dst
and L4 Src-port/Dst-port) as mentioned in below code snippet, the RSS algorithm
does not check for the IP fragmented packets.
It assumes all the incoming IP based packets will have L4-header and trying to
access the L4 Src-port/Dst-port fields using the pointer of L3-header
end-address without cross checking the L4 header presence. since, in-case of
fragmented packets the L4 header will not be present expect for first fragment
and thus should not consider L4 Src-port/Dst-port under the 4-tuple hash
calculation.
So, this RSS hash calculation has a bug in-case of fragmented packets.
File-name: ./drivers/net/tap/tap_bpf_program.c
================ =========================
rss_l3_l4(struct __sk_buff *skb)
{
.....
.....
__u8 *src_dst_addr = data + off + offsetof(struct iphdr, saddr);
__u8 *src_dst_port = data + off + sizeof(struct iphdr);
struct ipv4_l3_l4_tuple v4_tuple = {
.src_addr = IPv4(*(src_dst_addr + 0),
*(src_dst_addr + 1),
*(src_dst_addr + 2),
*(src_dst_addr + 3)),
.dst_addr = IPv4(*(src_dst_addr + 4),
*(src_dst_addr + 5),
*(src_dst_addr + 6),
*(src_dst_addr + 7)),
.sport = PORT(*(src_dst_port + 0),
*(src_dst_port + 1)),
.dport = PORT(*(src_dst_port + 2),
*(src_dst_port + 3)),
};
....
....
}
=========================================
So, here we can see the L4 src/dst ports were fetched without cross-checking
the packet has L4 header and in-case of fragmented packets the L4 src/dst ports
will be some junk values.
Due to this all the fragments of same packet were landing on to different
queues and thus re-assembling the fragments got failed.
Tested with DPDK-version "20.11.2" and the Linux Kernel-version is "5.4.17".
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